1. Field of the Invention
The present invention relates to initial adjustment circuits and initial adjustment methods of a magnetic bearing apparatus. More specifically, the present invention relates to an initial adjustment circuit and an initial adjustment method used for initially adjusting offset amounts and gains of a plurality of position sensors in a magnetic bearing apparatus used for a vacuum pump for obtaining a high vacuum or the like for magnetically supporting a rotational shaft of a spindle for a turbo molecular pump.
2. Description of the Background Art
FIG. 4 is a view showing a structure of a conventional magnetic bearing spindle. Referring to FIG. 4, a magnetic bearing spindle for turbo molecular pump 1 has a rotational shaft 3 provided in a case 2. Rotational shaft 3 is supported in a non-contact manner in thrust and radial directions by a thrust magnetic bearing 4 and radial magnetic bearings 5 and 6 respectively provided above and below magnetic bearing 4, and rotationally driven by a driving motor 7. A position in a radial direction of rotational shaft 3 is detected by radial position sensors 8 and 9, and a position in a thrust direction is detected by a thrust position sensor 10. Further, ball bearings for protection 11 and 12, which support rotational shaft 3 in case of abnormality of radial magnetic bearings 5 and 6, are arranged above and below rotational shaft 3.
Detection outputs from position sensors 8, 9 and 10 are applied to a controller 20 which is externally provided. Controller 20 controls magnetic bearings 4, 5 and 6 under control of an external system controller 30. As motor 7 is driven, rotational shaft 3 of magnetic bearing spindle 1 rotates.
In magnetic bearing spindle 1 shown in FIG. 4, when offset amounts and sensor gains of the outputs from position sensors 8, 9 and 10 are different from designed values, rotational shaft 3 is vibrated to be in contact with bearings for protection 11 and 12, whereby stable rotation is not ensured. To avoid this problem, the offset amounts and gains of position sensors 8, 9 and 10 must be precisely measured for adjustment.